(1) Field of the Invention
The present invention relates generally to archery equipment and more particularly pertains to improved compound bows.
(2) Description of the Prior Art
Archery bows in their simplest form are of unitary construction and are formed to include a bow handle, upper and lower resilient limb portions extending therefrom, and a bowstring attached to the upper and lower limbs.
In operation, as the archer draws the bowstring, the upper and lower limbs are flexed and potential energy is stored therein. When the archer releases the bowstring, the stored energy in the limbs propels the bowstring and the arrow nocked therein forwardly. The greater the energy required to flex the limbs the greater will be the energy available to propel the arrow when the bowstring is released. Arrow acceleration, arrow speed, the distance the arrow will travel, and the force with which it will strike the target are directly related to the force with which the arrow is initially launched. It is thus desirable to increase the amount of energy stored in the bow limbs so as to increase the force available to propel the arrow. Compound bows, in general, are able to store significantly more energy in their bow limbs than are simple, non-compound bows having long, more flexible limbs. However, the bending moments produced by the relatively widely separated bow limbs of compound bows are large and commonly require larger, more massive cast, forged or machined risers formed with handles or hand grips. Such risers have typically been constructed of lower strength materials such as wood, metallic composites of magnesium, and aluminum, the latter of which were formed by shaping, casting or forging. But because these lower strength materials had to withstand the large bending moments produced by the flexure of the limbs, and since the grip was a portion of the load bearing member, more riser mass was required to achieve the desired strength. An exception was the use of high strength aluminum forgings to produce bow handles, but only limited handle designs could be produced in this manner. Moreover, the fabrication process to produce such forgings was expensive and, in addition to the initial tooling expenses as, for example, to change the length of a bow riser, required extensive additional expense.
Since archery bows, particularly those used for hunting, were required to be both lightweight and portable, the low strength prior art compound bow risers of increased weight had distinct disadvantages. The relatively lightweight, high strength aluminum forged handles, capable of operating at higher stress levels, on the other hand, were not commercially practical. In addition, because the physical characteristics of the materials constituting bow riser components could not be accurately predicted, the components were over designed to assure adequate strength and to compensate for inherent design inaccuracies. That over design, however, resulted in heavier bows and attendant increased manufacturing costs.
Other types of lighter weight compound bow risers are disclosed in U.S. Pat. Nos. 4,756,295 and 4,759,337. The riser of the '295 patent is a single sturdy strap bent to either side or two straps secured together at the top and bottom and bowed apart at the center. The riser is connected to the limbs through a pivot point by a bolt. The riser of the '337 patent includes upper and lower sight windows 22 and 24 which are defined by upwardly and downwardly converging thin plate walls. Both of these risers differ significantly from the tubular structure of the instant invention in structure and the manner of producing the risers. In addition to the foregoing, U.S. Pat. Nos. 4,457,287, 3,055,353 and 4,124,014 show adjustable hand grips. These patents do not disclose or suggest the combination of a tubular riser assembly and an adjustable hand grip.
There are also known simple bows which were constructed of separable elements wherein the limbs were connected by tubular handles or couplers. See, for example, the tubular couplers disclosed in the simple non-compound bows disclosed in U.S. Pat. Nos. 2,608,188, 2,000,832, 1,877,273, 1,853,294 and 3,566,853. The tubular couplers disclosed therein join relatively flexible limbs in abutting relationship at their free ends. Since the limbs are highly flexible and the separation, if any, between the limb ends is small, the bending forces imposed on the tubular coupler are minimal. For this reason, the simple non-compound bow tubular couplers were able to be formed of thin walled, low strength materials. However, the tubular couplers of the simple non-compound bows were never required to withstand the large bending forces such as produced when the limbs of a compound bow are flexed, and tubular couplers were never used in compound bows. The single tubular riser 10 of the recurvature bow disclosed in the '853 patent is formed with an apex 13 so as to be generally "V" shaped. Such a shaped riser is less resistant to the bending forces and for that reason would be unsuitable for use with a compound bow having relatively stiff limbs. The foregoing structural differences patentably distinguish this cited patent from the instant invention.